The widespread diffusion of portable electronic devices, such as, mobile telephones, PDAs, or portable personal computers, including a plurality of integrated systems powered by batteries, has directed research towards approaches that allow a greater reduction in power consumption to prolong their operative functioning. To achieve this goal, reduction of the operating voltage (voltage scaling) of the components included in portable electronic devices has been started, which has made it possible to develop low power consumption systems.
However, due to some operative specifications, it may not be possible to reduce the operating voltage of some of the electronic systems included in a portable integrated electronic system, such as, for example, EEPROM and FLASH type memories, which typically require absolute voltage values (both positive or negative in sign). These absolute voltage values are typically higher than the voltage value that supplies the portable integrated electronic system where they are integrated, to properly perform the write and erase operations.
To address this, integrated electronic circuits known as voltage boosters have been produced. A voltage booster is a circuit that generates a voltage higher than the absolute value of the voltage supplied thereof. The most diffused type of voltage booster may be a charge pump. Charge pump voltage boosters, or more simply charge pumps, are formed by a plurality of cascaded multiplication stages, each including a corresponding pumping capacitor. The operation of a charge pump is based on charge maintaining and transfer phases in the sequence of pumping capacitors, which are interconnected through a corresponding switching elements, such as MOS transistors or diodes.
In particular, each pumping capacitor has a plate connected to a free terminal, which is controlled by a control signal that periodically switches between a low voltage and a high voltage. The control signals of pumping capacitors of adjacent stages are in mutual phase opposition. In this way, in the case of positive charge pumps (i.e. configured to provide a positive output voltage) when the control signal is at the low voltage value, the pumping capacitor is charged by the pumping capacitor of the previous stage in the cascade of multiplication stages. When the control signal switches to the high voltage value, an accumulated electric charge is transferred to the pumping capacitor of the next multiplication stage in the cascade. Conversely, in the case of negative charge pumps (i.e. configured for providing a negative output voltage) when the control signal is at the low voltage value, the pumping capacitor receives a charge accumulated in the pumping capacitor of the next multiplication stage in the cascade. When the control signal switches to the high voltage value, the accumulated electrical charge is transferred to the pumping capacitor of the previous multiplication stage in the cascade.
Each multiplication stage included in a charge pump is configured to provide, at its output, a multiple (positive or negative in sign) of a pump voltage provided by the integrated electronic system (e.g., the supply voltage). In more detail, the absolute value of an output voltage of a multiplication stage subsequent the first charge pump is typically equal to the pump voltage multiplied by the number of the previous multiplication stages of the charge pump plus one. Consequently, the voltage supplied by the charge pump increases substantially linearly with the number of multiplication stages within the same.
The pumping capacitor of each multiplication stage is located by the output terminal of the same stage to output the voltage corresponding to the electric charge accumulated on its plates. Consequently, at any stage subsequent a first multiplication stage of the cascade of multiplication stages, the value of a potential drop that is developed between the terminals of the pumping capacitor is substantially equal to the output voltage value of the multiplication stage, and increases substantially linearly with the number of multiplication stages. Such potential drop may become higher than a maximum voltage value that usually defines a limit of an area of safe operation, or SOA (Safe Operating Area).
The SOA is defined as the set of current and voltage conditions for which an integrated electronic system can function without being subjected to excessive stress or suffer irreparable damages. In more detail, the SOA is limited by a maximum voltage value and by a maximum current value, the product of which provides a safe operating maximum power. In addition, electronic devices operating in proximity of such voltage and/or current values suffer a reduction of their useful life due to the stress they are subjected.